(a) Field of the Invention
The present invention is related to an improved structure of a LCD optical wave-guide device, and more particularly to a backlight module free of dark bands and bright bands.
(b) Description of the Prior Art
As illustrated in FIG. 1 of the accompanying drawings for a sectional view of the structure of a backlight module for an LCD of the prior art, the backlight module is essentially comprised of a reflector mask 10, multiple light sources 20, a diffuser plate 30, a lower diffuser sheet 40, a prism 50, a reflective polarizing sheet or an upper diffuser 60 and a protector sheet 70 arranged in sequence from inside out. Wherein, the light sources 20 may be each a light tube in the shape of a stripe, U-shape or other continuous curve arranged at a proper spacing between the reflector mask 10 and the diffuser plate 30 and the light emitted by each of the light sources 20 provide the display effects by the LCD. Therefore, the diffuser plate 30 functions to diffuse the light passing through it to correct the dark bands and the bright bands created on the LCD due to the absence of light produced at each spacing between two abutted sources 20.
Whereas the diffuser plate 30 functions only to help achieve the even diffusion for light passing through it, it has a limited efficiency in correcting the phenomenon of the bright bands and the dark bands observed on the LCD. An improvement is made for certain backlight modules by extending the distance between the light source 20 and the diffuser plate 30 in the hope of widening the scope of each of those light sources 20 entering into the diffuser plate 30 to achieve the purpose of reducing the dark bands. However, the structural design for such an improvement not only provides limited effects but also results in a backlight module which must be made thicker thereby failing the compact requirements in the current LCD market.
Furthermore, some other backlight modules seek to provide extinction (dispersion) on the surface of the diffuser plate by printing on the diffuser plate with ink containing SiO2 or TiO2 to achieve the purpose of reducing the dark bands. Again, the extinction process not only increases the production cost of the diffuser and the complexity of the manufacturing process, but also relates to a passive solution to reduce the dark bands on LCD since the extinction occurs only after the light lands on the surface of the diffuser.